This is a nationalization of PCT/SE01/00654, filed Mar. 30, 2001 and published in English.
1. Field of the Invention
The invention relates to a clutch arrangement for rapid disengagement of two elements in a transmission system when a chosen torque is exceeded. One element is a conical shaft end that carries a corresponding sleeve which, in turn, carries externally at its axial ends two mutually spaced ball bearings and a force transmission ring disposed therebetween. An annular force transmission body surrounds and is carried by the ball bearings and includes a pressurizable hydraulic chamber which when pressurized through the medium of a valve on the body, causes the diameter of the inner surface of the body to decrease so as to attain force transmitting engagement with the outer surface of the ring. The sleeve carries a dogging element which is adapted to act on an element carried by the body for relieving the hydraulic chamber of pressure upon relative rotation between the body and the sleeve. Such a clutch arrangement functions to mutually disengage two transmission components mutually connected via said clutch arrangement, at a predetermined moment in time.
2. Description of the Related Art
Clutch arrangements of this particular kind are sometimes called safety couplings and are well known from WO 97/21044 for example. Such clutches, or couplings, are often used in transmissions with which heavy loads are transmitted, for the purpose of protecting the equipment on the driving and/or on the driven side of the transmission against damage that can occur if the torque transmitted through the transmission and the clutch exceeds a threshold value. Clutches of this particular kind shall break the load transmission with the minimum of damage to the clutch or coupling itself, so that the clutch can be replaced quickly and easily and/or repaired.
However, the axial length of the space incorporated for accommodating the safety coupling is sometimes restricted. This results in special problems that must be solved, since it may otherwise be necessary to make significant changes in other parts of the transmission in which the clutch shall be fitted.
One example in this respect is that each carriage of existing express trains of a given design has an individual electrically driven motor at one end of the carriage. The output shaft of the motor is short and is coupled to a first universal joint via a long rod and a second universal joint connected thereto, to a distribution gear situated at the other end of the carriage and having two output shafts which are each connected to drive a respective wheel in a wheel pair. The transmission as such has long been tested and it is, of course, suitable to mount a clutch or coupling arrangement at a position in the transmission in which the transmission is influenced to a minimum by the inclusion of the clutch arrangement and so that the clutch arrangement is positioned conveniently with respect to fitting and removing said arrangement to and from the system. This means that in such instances the clutch will preferably be mounted between the output shaft of the motor and the universal joint proximal thereto. The problem that arises in the majority of cases is that the shaft obtains a length which is smaller than its diameter.
A further problem is that the hydraulic pressure of the clutch must be in the order of 1000 bar. The clutch typically includes a ring-shaped body that has a coaxial, cylindrical hydraulic chamber, such that the inner wall of the body will move radially inwards when the chamber is pressurised and thus obtain a reduction in diameter, wherewith the inner wall is brought into engagement with a sleeve that has a conical inner surface and that is driven up onto the conical end of the motor shaft.
When the hydraulic chamber is not pressurised, the body is able to rotate relative to the sleeve on ball bearings disposed between the body and the sleeve as there will then be a radial clearance between the body and the sleeve. The body includes a valve via which the hydraulic chamber is pressurised. The sleeve is a dogging element which upon relative rotation of the body with the sleeve functions to break-off a shear-pipe that communicates with the chamber, so as to depressurise the hydraulic chamber and thereby rapidly break the power transmission between the body and the sleeve so as to ensure minimum damage to the clutch and to the transmission elements connected thereto.
Because of the small axial space in which the clutch arrangement is housed, the hydraulic pressure must be high, e.g. 1100 bar, in order to achieve requisite torque transmission. Pressures of such high magnitudes will, of course, constitute a break-down hazard. Moreover. the difficulty in providing for comfortable fitting and removal of the body and bearings to and from the sleeve presents a problem.
The object of the present invention is therefore to provide a clutch arrangement with which high torque transmission can be achieved despite a short axial length, and that can be readily fitted and removed to and from the sleeve, and that can also operate at relatively low hydraulic pressures.
This object is achieved by the invention of a clutch arrangement for rapid disengagement of two elements in a transmission system when a chosen torque is exceeded. One element is a conical shaft end that carries a corresponding sleeve which, in turn, carries externally at its axial ends two mutually spaced ball bearings and a force transmission ring disposed therebetween. An annular force transmission body surrounds and is carried by the ball bearings and includes a pressurizable hydraulic chamber which when pressurized through the medium of a valve on the body, causes the diameter of the inner surface of the body to decrease so as to attain force transmitting engagement with the outer surface of the ring. The sleeve carries a dogging element which is adapted to act on an element carried by the body for relieving the hydraulic chamber of pressure upon relative rotation between the body and the sleeve. The ring and the body are adapted to pass free from each other when the hydraulic chamber is depressurized, the ring being connected operatively with the sleeve so that relative rotation between the clutch components takes place between the ring and the body when the clutch is triggered.
Further embodiments of the inventive clutch arrangement will be apparent from the accompanying dependent claims.
The invention resides in positioning the ball bearings beneath the axial ends of the body, and by operatively connecting to the sleeve a ring that extends up to the inner surface of the body. The ring can be connected operatively with the sleeve, by giving the mutual co-acting surfaces of the ring and the sleeve a relatively high coefficient of friction, for example by forming ridges or by applying a hard powder, e.g., tungsten carbide powder, on one of the surfaces, for instance on the inner surface of the ring. The ring will then be essentially free from the sleeve when the hydraulic chamber is depressurised and when the sleeve is withdrawn from the end of the shaft, so that the body, the ball bearings and the ring can be readily withdrawn axially from the sleeve. The sliding surfaces of the clutch arrangement, i.e. the mutually facing surfaces of the body and the ring, may be damaged as a result of frequent activation or engagement of the clutch due to exceeding a set torque, and the heavily loaded ball bearings may also be damaged as a result of unbalanced forces. It is therefore appropriate to replace such components so as to bring the clutch to an operable state.
The ring may be fixedly connected to the sleeve, the construction should then be further developed so as to enable the bearings to be dismantled by moving them towards respective axially adjacent ends of the body, wherewith the dogging element, which is suitably located axially outwards of one of the ball bearings, should be capable of being dismantled.
Alternatively. the ring may be removably connected to the sleeve via a spline connection or some other known type of connection, so as to enable the body with the ball bearings and the ring to be readily withdrawn axially from the sleeve when removed from the shaft, after having loosened the connection.
In a further variant of the invention, the dogging element may include a hub fitted to an end-part of the sleeve so as to lock onto the sleeve when said sleeve widens as it is driven onto the conical shaft end, thereby enabling the dogging element to be readily dismantled or removed when the sleeve has been withdrawn, wherewith the ball bearings can be readily removed axially towards respective adjacent ends of the sleeve, whereby the ring may be fixed to the sleeve, and whereby the sleeve and the ring constitute a replacement for restoring the clutch to an operative state.
In preferred embodiments, the respective axial ends of the hydraulic chamber are situated approximately in a plane that is normal to the clutch axis, containing centres for the balls of respective ball bearings. In this way, the end-part of the annular body will swing out so that the outer rings of the ball bearings are also twisted when the hydraulic chamber is pressurised, whereby the ball bearings are controlled and swing-in between their bearing races with no clearance or play. This avoids so-called xe2x80x9cbrinellingxe2x80x9d otherwise caused by balls that lie in the gap between races bouncing against each other as a result of external vibrations between the bearing rings and causing microscopic damage thereto. Because a clutch. or coupling, according to the invention may be in use for a considerable time (several years) before the clutch is triggered, such vibrational damage can develop over a long period of time and significantly reduce the life-time of the ball bearings, so that they will not be operable during the short period of time that the body and the sleeve rotate relative to each other when the clutch is triggered. Because of the clearance-free clamping of the balls of the bearings, the useful life of the ball bearings is increased without needing to use ring-shaped spring elements that would encroach on the axial space required for accommodating the length of the ring in the space at disposal for the clutch arrangement.